This invention relates generally to data communication in a network of computer systems. More particularly, it relates to a communication endpoint structure which enables application programs resident on systems to communicate through such a network irrespective of the protocol for which the application was written and the protocols available on the network.
Once upon a time, almost all computer systems were standalone processors to which private peripheral devices such as displays, printers and disk drives were connected, acting independently from any other computer system. Yet, it became apparent that there were substantial gains to be made if several computer systems could be cooperatively coupled together. Today, it has become commonplace to couple a multitude of computer systems into a distributed environment such as a local area or wide area network.
However, there are many vendors who have developed their own hardware and software solutions for integrating multiple computer systems. In particular, they have developed different ideas of the format and protocols that should be followed in transporting data through the networks. Some protocols support expedited data transmission by bypassing the standard data flow controls; others require all data to go through the controls. Specialized protocols are used for transport tasks such as establishing and terminating connections between computer systems. Examples of well known communication protocols include System Network Architecture (SNA), Digital Network Architecture (DECnet), Transmission Control Propotocol/Internet Protocol (TCP/IP), Network Basic Input/Output System (NetBIOS), Open Systems Interconnection (OSI) and AppleTalk. Other protocols are known and widely used.
Most distributed application programs are written to an application programming interface (API) which assumes a particular communications protocol. However, the distributed environments which most organizations have assembled are quite complex, comprised of confederations of individual networks running different communication protocols. If the transport protocols assumed by the distributed application's API and the transport protocols actually implemented in one or more of the networks on which the organization would like to send its data are not the same, the use of the application is limited. The problems of such heterogeneity in communications protocols is expected to get worse as more organizations begin to communicate with each other through their networks to perform order processing, direct billing or other cross organization activities.
While the distributed applications could be rewritten so that they can run over each transport protocol or application gateways can be written for each distributed set of distributed applications, the cost of having programmers write all the necessary code makes these approaches economically unattractive. A preferred solution is presented in commonly assigned patent, U.S. Pat. No. 5,224,098, entitled "Compensation for Mismatched Transport Protocols in a Data Communications Network", by R. F. Bird et al, filed Jul. 17, 1991 and hereby incorporated by reference. The incorporated patent teaches a transport connection layer between a first transport user at one node in the network and a second transport user at a different node in the network. When the transport protocol assumed by the application at the first node is not available in the network, the data being transferred between the two nodes is automatically altered to be compatible with the available transport protocols. Thus, an organization is able to choose application programs solely on the basis of the functions they provide, rather than the protocols which they require.
The above referenced application teaches a generalized transport layer. One of the transport structures which is presently used in the Berkeley version of the UNIX.TM. environment is called a socket. A socket is an object that identifies a communication endpoint in a network. A socket hides the protocol of the network architecture beneath from the application. A socket allows the association of an endpoint, such as an application program, with one of the selected protocols. This association occurs when the endpoint is created. An endpoint creation implies a static association of the socket with the protocol, which will remain invariant. However, in a multiprotocol environment, as described in the above referenced application, which facilitates heterogeneous connectivity, a transport endpoint may need to be bound to any of several available protocols after the creation of the endpoint. Therefore, if sockets are to be used in such an environment, a new socket structure which allows dynamic association of the socket with the protocol must be devised. The present invention teaches such a socket structure.